Magazines for firearms are used to assist in chambering cartridges into the breech of the firearm and are typically designed to hold a fixed quantity of cartridges. The capacity of a magazine is generally a function of the length and width of the magazine and the space consumed by the spring and follower used to move cartridges through the magazine housing.
Some of the states of the United States have enacted specific limits on cartridge capacity of magazines and these limits are not uniform among these states. Generally, the solution invoked to lower the capacity of a magazine involves physically reducing cartridge storage space within the magazine. Aftermarket solutions for reducing magazine capacity typically involve adding a plug to the magazine to prevent the magazine from holding more than the desired quantity of cartridges.